Incorporating metabolic labels into their corresponding biopolymers is greatly facilitated by minimizing the size of artificial residues. Since linear alkenes such as vinyl moieties are small and undergo inverse electron demand Diels-Alder (iEDDA) reactions with tetrazines, they are particularly interesting for bioorthogonal labeling. Pyrimidyl tetrazines show a well-balanced equilibrium between chemical stability and reactivity that helps to overcome the inherently low reaction rates of linear alkenes. Compared with traditionally applied tetrazines, pyrimidyl tetrazines stand out for their
Scheme 1: Pyrimidyl tetrazines are particularly reactive dienes in iEDDA due to the direct linkage of the tetrazine core to the electron-withdrawing pyrimidine ring. Applications include the conversion of alkene-decorated sugars[1,2], amino acids and nucleotides[4,5], thus permitting bioorthogonal labeling of glycanes, proteins and nucleic acids at rate constants of 0.01 – 0.1 M-1s-1.
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| Niederwieser et al. (2013) Two-color glycan labeling of live cells by a combination of Diels-Alder and click chemistry. Angew. Chem. Int. Ed. Engl. 52 (15):4265.
 Späte et al. (2014) Rapid labeling of metabolically engineered cell-surface glycoconjugates with a carbamate-linked cyclopropene reporter. Bioconjug. Chem. 25 (1):147.
Single-step and two-step life cell labeling of terminal alkenes on glycanes
| Lee et al. (2014) Genetically encoded unstrained olefins for live cell labeling with tetrazine dyes. Chem. Commun. (Camb). 50 (86):13085.||Application:
Labeling of bacterial membrane proteins
| Busskamp et al. (2014) Efficient labelling of enzymatically synthesized vinyl-modified DNA by an inverse-electron-demand Diels-Alder reaction. Chem. Commun. (Camb). 50 (74):10827.
 George et al. (2017) Vinyluridine as a Versatile Chemoselective Handle for the Post-transcriptional Chemical Functionalization of RNA. Bioconjug. Chem. 28 (5):1529.
In-vitro-labeling of DNA and RNA